This invention relates to an apparatus and a method of identifying and classifying the minutia of a fingerprint for the purposes of enrollment to establish a reference file and verification of a subject's identity against his or her reference files.
Fingerprints are uniquely identified by the set of minutia characteristic of the fingerprint. These minutia are two standard elements; line endings and line bifurcations. A fingerprint can be analyzed either in terms of its ridges or its valleys. In either case, there will be endings and bifurcations. Specifically, the ridge analysis of a fingerprint will be in terms of ridge endings and ridge bifurcations while a valley analysis of a fingerprint will be in terms of valley endings and valley bifurcations. Indeed, a valley ending is defined by a ridge bifurcation and a ridge ending is defined by a valley bifurcation.
In this application, it will be convenient to assume a ridge ending and bifurcation analysis and thus all references in this disclosure, unless specifically otherwise indicated, will be to ridge endings and ridge bifurcations. However, it should be understood that the use of the terms line endings and line bifurcations in the claims is generic to both the ridge and valley analysis.
In addition to the line endings and bifurcations there are all sorts of line breaks, bridges and other irregularities in a typical fingerprint which deviate from an ideal conception of a pattern of sworls and lines having only classical minutia (line endings and bifurcations) to characterize the pattern. These other characteristics will be deemed fingerprint noise herein. This fingerprint noise tends to be unstable from one fingerprint scan to another. The classical minutia tends to be stable. But bridges, breaks, ripples, cracks, holes and other characteristics of a given fingerprint tend to disappear and reappear from one finger impression to another. Thus these characteristics, deemed noise herein, are a main reason why it is difficult to use optical or electronic systems, or a combination thereof, for automatic analysis or identification of a fingerprint.
It is a purpose of this invention to provide a technique of efficiently distinguishing between classical minutia and noise.
There are two types of errors which it is the object of this invention into minimize. These errors will be termed herein Type I and Type II errors. For example, in a system used to screen access to a room, a Type I error is one where the individual who is supposed to have access is rejected. A Type II error is one in which an individual who is supposed to be denied access is passed. Thus a Type I error can be considered a false negative and a Type II error can be considered a false positive.
More generally, low Type I errors indicate system sensitivity in that the system is sensitive to the correspondence between an input fingerprint and the corresponding enrolled fingerprint. Thus, in a high percentage of cases, the system will positively identify the individual whose fingerprint is being presented.
Similarily, low Type II errors indicate system specificity in that the identification is specific to the individual involved so that the probability is low that an input fingerprint will be identified as corresponding to an enrolled fingerprint of another individual.
It is a further purpose of this invention to provide a system which will have low Type I errors and low Type II errors in combination with fast verification of an input fingerprint and to do so employing equipment and apparatus having a cost that warrants relatively wide spread use.
It is another purpose of this invention to provide an optimum trade-off between (a) selecting a portion of the fingerprint minutia for use in encoding a fingerprint to minimize the time it takes to complete a verification routine and (b) maintaining enough minutia information in the enrolled file to minimize Type I and Type II errors.
U.S. Pat. No. 4,322,163 is incorporated herein by reference. It discloses a preferred optical scan technique for developing the fingerprint configuration that is processed by the fingerprint identification system of this invention.